Device for mechanically clamping a stack comprising electrochemical cells

Abstract

The invention relates to a device for mechanically clamping a stack comprising electrochemical cells, - wherein the stack has a pair of end plates which are held against one another via a clamping means in such a way that the stack with its electrochemical cells can be clamped between the end plates, - wherein the clamping means is designed to exert a clamping force with the end plates on the stack arranged between the end plates, - and the clamping means serves as an electrical conductor for the electrochemical cells in the stack.

Description

[0001] Device for mechanically clamping a stack with electrochemical

[0002] cells

[0003] The present invention relates to a device for mechanically clamping a stack of electrochemical cells that can be used for electrolysis or as a fuel cell. A stack consists of a plurality of repeating units of electrochemical cells connected in series.

[0004] SOEC electrolysis stacks (Solid Oxide Electrolyzer Cells = SOECs) feature glass-sealed repeating units made of metal parts and ceramic SOCs. Operation requires mechanical tension to prevent the glass seal between the metal parts from separating or breaking. Mechanical tension is also necessary in alkaline electrolyzers.

[0005] Several clamping methods are known for applying the clamping force when the stack is cold: One method uses a transport clamp consisting of metal parts, which is typically removed after transport and before installation of the stack in high-temperature electrolyzers. In this case, an installation and removal clamp consisting of plastic straps can maintain the clamping force until a process clamp intended for the hot state is applied to the stack. Furthermore, it is known for high-temperature electrolyzers to use an installation and removal clamp consisting of plastic straps when switching between the transport clamp and the process clamp, which maintains the clamping force during the changeover; this installation and removal clamp can, for example, burn away during operation at higher temperatures.A device for detecting oxidation in a fuel cell is known according to US 2018 / 0175418 Al. It is designed to measure the height of the fuel cell stack, for which purpose a mechanism is attached to the fuel cell stack that measures any increase in height compared to a previously measured height value and correlates this with oxidation in the fuel cell stack.

[0006] From JP 2011 198 546 A, a power generation unit is known that comprises a flat solid oxide fuel battery cell; a control unit is provided with a first loading mechanism that applies a load to the power generation unit that does not damage the component, even when it is operated normally for a long period after an initial reduction; furthermore, a second loading mechanism is provided that applies an additional load to the power generation unit. The mechanical tension is applied via bolts.

[0007] An arrangement and method for stack compression are known from US 2011 / 0076585 Al, wherein a guide plate is configured to apply a load to a stack of electrochemical cells, with compression or mechanical stress being achieved by springs.

[0008] In WO 2007 / 112728 Al, a temporary clamping device is specified which consists of a plastic material and burns at the operating temperature of a SOC.

[0009] EP 1 879 251 A1 discloses a compression arrangement for distributing an external compressive force onto a solid oxide fuel cell stack, wherein the compression arrangement comprises a force distribution plate and a force distribution layer, such that the external compression arrangement is mounted together with the solid oxide fuel cell stack, and the external compression force is exerted on the force distribution plate. Overall, a compression arrangement is disclosed which achieves force distribution by means of elastic elements such as metallic springs and plates at both ends of the stack.

[0010] According to EP 3 625 846 A1, an electrochemical device is known that operates as a SOEC electrolysis or co-electrolysis reactor or a SOFC fuel cell at high temperature. The known device comprises the following: a stack of SOEC / SOFC-type solid oxide electrochemical cells; two end plates, so-called end plates, between which the stack is arranged; two clamping plates of the stack, between which the end plates and the stack are arranged;

[0011] Clamping means between the clamping plates, wherein the clamping means are suitable for clamping and holding the stack between the end plates, regardless of the temperature between the ambient temperature and the high operating temperatures of the device; a clamping chamber bounded between one of the end plates and the adjacent clamping plate, wherein the clamping chamber is connected to a clamping gas circuit at positive pressure relative to the interior of the stack.

[0012] From US 20090114531 Al or EP1908145, a cell stack is known with at least one electrochemical cell arranged between a first end plate connected to an electrical bolt and a second end plate connected to another electrical bolt, wherein the stack comprises a housing, a device for providing a fixed support of the cell stack on the housing, and a device for maintaining a constant mechanical load over the cell stack, wherein the device for maintaining a constant load comprises at least one elastic cushion inserted into the space between the cell stack and the housing wall.

[0013] From US 20070015039, a fuel cell is known with electrolyte electrode assemblies and separators, wherein each assembly contains an anode, a cathode, and an electrolyte. The separators generate multiple fuel gas flow fields for the anodes and oxygen-containing gas flow fields for the cathodes. The claim is characterized in that it has multiple electrolyte electrode assemblies per separator, wherein slots divide the separator area into sections corresponding to the assemblies, and that it includes a mechanism for applying a tension load, which applies a greater load near the fuel gas supply unit than on the assemblies themselves. Preferred embodiments describe features such as the inclusion of an exhaust duct, the structure of the separators, and specific shapes of projections on the separators.

[0014] According to US 2023317976 Al or EP4205210, an electrochemical cell arrangement is known comprising a base plate (308) and a top plate (303), between which a stack of planar cell units (306) and at least one positive and at least one negative electrical end plate (302, 310) are arranged under pressure by means of compression means (307) acting between the base plate (308) and the top plate (303). At least one of the electrical end plates (302, 310) is connected to or integrally formed with an electrical stud (301) extending from a base section of the at least one electrical end plate (302, 320) and passing through an opening in the base plate (308) or the top plate (303) to form an electrical connection.wherein a fluid seal is maintained by the compression means (307) between the base section and the respective base plate (308) or cover plate (303) to prevent fluid loss through the opening; wherein cell units in the stack of planar cell units (306) are provided with at least one opening and are stacked one above the other such that the respective openings are aligned to form a respective inner distributor extending through the stack (306), and wherein the electrical bolt (301) extending through its respective opening is also aligned with the respective inner distributor, so that the compression forces exerted by the compression means (307) to seal the respective inner distributor also act to seal the respective opening.

[0015] The invention is based on the objective of providing a device for mechanically clamping at least one stack of electrochemical cells, which facilitates the handling of stacks during transport, installation, removal, and operation using simple means. Advantageous embodiments are the subject of the dependent claims.

[0016] The device according to the invention has the features of claim 1. Accordingly, the device is suitable and designed for mechanically clamping at least one stack with electrochemical cells as repeating units. The stack has a pair of end plates which are held together by a clamping device such that the stack with its electrochemical cells can be clamped between the end plates. The clamping device is designed to exert a clamping force on the cells arranged between the end plates. According to the invention, the clamping device is designed as an electrical conductor for the electrical cells in the stack and also serves as an electrical conductor for the stack. By using the clamping device as an electrical conductor, it is possible to use the device for mechanically clamping the stack both during transport and during operation of the stack.Previous devices for clamping the stack required connecting electrical conductors to the stack after installation, necessitating welding within the electrolysis plant. This welding process required switching from transport clamping to operational clamping – that is, from a design that facilitates transport at room temperature to a design that provides mechanical clamping during operating temperatures, such as high-temperature electrolysis. By using the clamping device as an electrical conductor for the stack, as in the invention, the step of subsequently attaching the electrical conductors to the stack is eliminated. This allows for continuous clamping of the stack, suitable for both operation and transport.

[0017] Preferably, at least one spring assembly is provided, which exerts the clamping force on the stack arranged between the end plates via at least one of the end plates. An advantage of the spring assembly is also that temperature-related changes in length can be compensated for and a constant spring force can be applied.

[0018] In a preferred embodiment, the pair of end plates comprises a stack base plate and a stack top plate. One of the two end plates is in electrical contact with the clamping device. Preferably, the clamping device can be connected to one of the end plates, thus establishing, for example, the electrical contact between the end plate and the electrical clamping device.

[0019] In a preferred embodiment, the other of the two end plates is equipped with an additional electrical conductor located on the side of the stack's top plate or bottom plate facing away from the stack, and this conductor makes electrical contact with the stack. Thus, the two end plates are accompanied by a clamping element that is in electrical contact with one of the two end plates (and therefore forms one pole), and by another electrical conductor located on the stack's top plate or bottom plate, which makes electrical contact (with the other pole) of the stack. In this way, both ends of the stack are contacted with electrical conductors via their poles, enabling the electrical connection of the stack to be established via two electrical conductors.

[0020] In a preferred embodiment, a bridge is provided through which the clamping device is guided. The clamping force is preferably applied uniformly to the cells by means of the bridge, which can be designed, for example, as a plate-shaped component, a strut, or a beam. Because the clamping device is guided through the bridge, the bridge can change its position relative to the clamping device in order to exert the desired clamping force on the stack.

[0021] In a preferred embodiment, the clamping device is connected to one of the end plates via the bridge for applying a clamping force. This applies particularly in the cold state, i.e., during the transport of the stack.

[0022] In a further preferred embodiment, the spring assembly is provided which is supported on the bridge and applies its clamping force to one of the end plates. Preferably, a damping element can be provided between the bridge and the spring assembly, particularly for the operating state. In this embodiment, the spring assembly then acts between the bridge and the damping element to apply the clamping force to one of the end plates.

[0023] The spring assembly supports the tension force and also has the advantage of being able to build up even pressure.

[0024] In a preferred embodiment, an additional clamping device is provided, designed as a housing for at least one stack. The housing has a tubular body and an additional cover, the cover exerting the clamping force on the bridge when attached to the housing. The housing ensures that the cover, when used to close the housing, acts as an additional clamping device on the bridge. The housing may also include a frame that allows for the holding and clamping of multiple stacks. In this case, each stack is mechanically clamped using the frame as an additional clamping device.

[0025] This additional clamping device can exert a clamping force on the bridge, supplementing, for example, the spring assembly. If the bridge is connected to the cover, a sensor can be arranged between the cover and the bridge in a preferred embodiment. The sensor can monitor various parameters of the stack; for example, it can also measure the mechanical clamping force. The sensor can also be arranged at a different location on the stack, in the housing, or on the frame.

[0026] In a preferred embodiment, a housing is designed for multiple stacks, and at least one stack is equipped with a stack clamping device that exerts the clamping force on the bridge. The clamping force is then exerted via the bridge on the other stacks arranged in the housing. In a preferred further development, the clamping device is equipped with two or more rods, in particular metal rods. The rods are designed such that the electric current can be conducted through them with low resistance, advantageously at high temperatures such as during the operation of a high-temperature electrolysis process.

[0027] The electrochemical cells in the stack are also preferably based on solid oxides of the SOEC / SOC type.

[0028] A preferred embodiment is explained in more detail with reference to the following figures. They show:

[0029] Figure 1 schematic representation of an embodiment of a mechanical clamping device according to the invention in a cylindrical housing and

[0030] Figure 2 shows the assembly from Figure 1 without the housing and electrical contacts.

[0031] The clamping device of Figure 1 has a stack base plate 10, to which a stack 12 is adjacent. The stack 12 consists of stacked repeating units sealed against each other by glass gaskets. The figure shows the size ratio between the stack and the clamping device for a stack with approximately 30 repeating units. The clamping device is also suitable for stacks with up to 900 repeating units. Two rods 14 are guided along the stack 12, spaced apart from the stack 12 and electrically connected to the stack base plate 10. During transport and handling, the two rods 14 serve to transmit the clamping forces to the stack and to the cells within the stack. They are dimensioned accordingly to exert a sufficient clamping force on the stack.In the operating state, the two rods 14 form the negative terminal conductor of the stack due to their mechanical contact with the stack base plate. The stack 12 with its electrical cells is connected to the stack base plate as the negative terminal of the stack 12.

[0032] The stack 12 is arranged between a pair of base plates, with a stack top plate 16 and a stack base plate 10 provided on both sides of the stack. A rod 18 is arranged on the stack top plate 16, which in operation serves as the positive current conductor of the stack 12. Furthermore, an insulation assembly 20 is provided, comprising a multi-layered structure of thermally insulating plates 22a, 22b, 22c. The insulation assembly 20 is provided with a support plate 24, which is in contact with a spring assembly 26. The spring assembly 26 rests at one end against the support plate 24 and at its other end against a bridge 28. The bridge 28 is designed to exert the clamping force on the stack 12 arranged between the stack base plate 10 and the stack top plate 16. For this purpose, bridge 28 is provided with bores through which the rods (negative pole conductors) 14 are guided.A clamping force can be exerted on the bridge 28 via a combination of nuts and sleeves 30. For this purpose, the rods (negative pole conductors) 14 are equipped with an external thread at their free end, onto which a nut 30 can be screwed. The bridge 28 presses via the spring assembly 26 onto the support plate 24, the insulation assembly 20, and the stack top plate 16. A separately designed pressure piece 32 can be provided between the insulation assembly 20 and the stack top plate, which transmits the force from the insulation assembly 20 to the stack top plate 16. To be able to remove the accumulated tensile force after transport of the stack 12, a tubular housing 34 is provided. The tubular housing 34 has a projecting annular flange 36 at one end, onto which a cover 38 can be screwed. A gas distributor 40 is provided at the lower end of the tubular housing 34 opposite the lid 38.After transport, closing the cover 38 exerts a pressure force on the bridge 28. A central pressure piece 42 can be provided to transmit the force of the cover 38, which is attached to the ring flange 36, to the bridge 28.

[0033] The tubular enclosure 34 can have closed or perforated walls, depending on its design. The tubular enclosure 34 has a diameter sufficient to accommodate the clamping device with the stack and the two rods (negative pole conductors) 14. Alternatively, a frame for holding the stack 12 can be provided instead of the tubular enclosure 34, offering the same functionality as the tubular enclosure 34 with regard to mechanical clamping.

[0034] Figure 2 shows the clamping device from Figure 1, wherein the insulating assembly 20 has two L-shaped interlocking elements 44a, 44b. The negative terminal conductors are connected via cables 46, 48 to electrical contacts 50 and 52 on the outside of the cover. The electrical contacts 50, 52 are attached to the outside of the cover 38 and can be contacted there. Also visible in Figure 2 is the electrical contact 54 for the positive terminal, which originates from the positive terminal conductor 18. The positive terminal conductor 18 is guided centrally through the spring assembly 26.

[0035] The clamping device according to the invention offers the advantages that work steps involving re-clamping before and during stack assembly and disassembly are eliminated. A further advantage is that a critical work step, such as welding electrical conductors to current contacts near the stack, can be omitted, since the rods 14 used for mechanical clamping can also carry current.

Claims

Claims 1. Device for mechanically clamping a stack of electrochemical cells, • wherein the stack has a pair of end plates which are held together by a clamping device in such a way that the stack with its electrochemical cells can be clamped between the end plates, • wherein the clamping device is designed to engage the end plates to exert clamping force on the stack arranged between the end plates, • and the clamping device as an electrical conductor for the electrochemical processes Cells in the stack serve this purpose.

2. Device according to claim 1, characterized in that at least one of the end plates exerts the clamping force on the stack arranged between the end plates via a spring assembly.

3. Device for mechanical clamping according to claim 1 or 2, characterized in that the pair of end plates comprises a stack bottom plate and a stack top plate, wherein one of the two end plates is in electrical contact with the clamping means.

4. Device for mechanical clamping according to claim 3, characterized in that the other of the two end plates has a further electrical conductor which is arranged on the stack top plate or the stack bottom plate and which has an electrical contact with the stack.

5. Device for mechanical clamping according to one of claims 1 to 4, characterized in that the clamping means is guided through a bridge.

6. Device for mechanical clamping according to one of claims 1 to 5, characterized in that at least one insulating element is arranged on one of the sides of the end plates facing away from the stack.

7. Device for mechanical clamping according to one of claims 1 to 6, characterized in that the clamping means is connected to the bridge for applying a clamping force to one of the end plates.

8. Device for mechanical clamping according to one of claims 2 to 7, characterized in that the spring assembly is supported on the bridge and applies the clamping force to one of the end plates.

9. Device for mechanical clamping according to claim 8, characterized in that the spring assembly acts between the bridge and the damping element and applies the clamping force to one of the end plates.

10. Device for mechanical clamping according to one of claims 1 to 9, characterized in that a further clamping means is provided, wherein the further clamping means is a housing having a tubular body and additionally a cover, wherein the cover in a state attached to the housing exerts the clamping force on the bridge or the further clamping means is a frame in a housing to accommodate and mechanically clamp several stacks.

11. Device according to one of claims 1 to 10, characterized in that the housing is designed for several stacks and at least one stack with is equipped with a stack clamping device for exerting the clamping force on the bridge.

12. Device for mechanical clamping according to claim 10 or 11, characterized in that the cover has a spacer on its side facing the stack, which rests against the bridge in the state of the cover being attached to the housing.

13. Device for mechanical clamping according to one of claims 1 to 12, characterized in that the clamping means has two or more rods, preferably metal rods.

14. Device for mechanical clamping according to one of claims 1 to 13, characterized in that the electrochemical cells are based on solid oxides of the SOEC / SOC type.

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